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Overall walk-around of the boot.

Picture 9 of 10.

The circular mark on the ball of the foot and the mark on the heel correspond to where Velcro pads would have been affixed. The Apollo Lunar Module News Reference notes that

The crew compartment deck (flight station floor) measures approximately 36 by 55 inches. Nonflammable Velcro pile is bonded to the decks' top surface; a hooked Velcro on the soles of the astronauts' boots provides a restraining force to hold the astronaut to the deck during zero-g flight.

A page on the Apollo Lunar Surface Journal has a series of photos of Neil Armstrong's Apollo 11 suit. The second photo on the page, S69-38889, shows the suit pre-flight, and has one of the boots turned to show the sole; the Velcro pads are clearly shown. That same page has a post-flight photo of the sole of the boot showing the Velcro patches. It's unclear as to whether the heel Velcro patch covers part of the metal heel clip on Armstrong's boot or whether the USSRC's boot has longer heel clip than the flight model of the boots.

The metal heel clip attached the boot to the command module couch's foot pan for leg restraint during launch and reentry.